Let's say I wanted to start an online magazine (with or without a podcast component). Let's say I came up with a cool name.

Now let's say that cool name exists already in another field. For example, museum/library science.

Obviously the best option is to come up with another name, but if I really want to use this name, is it just a matter of getting higher in the Google rankings than the other guys? Is it cool to have two magazines in disparate fields with the same name? Thoughts?

If there was another podcast with the same name? That'd be a problem, even if that other podcast was about something else entirely.

To the best of my knowledge, the other thing (let's call it Jones Magazine) is just a print magazine with a website, and they're focused on museums and library science. I would have Jones Magazine and Podcast or the Jones Podcast or something, and I would be focused on fiction.

I think you'd need some differentiation - if there's a Jones Magazine of library science, you can't have a Jones Magazine of fiction. Especially if they've trademarked the name as then they'll be within their rights to sue you out of existence.

However, you probably could have the Jones Fiction Magazine or something like that without too much trouble, unless they have very trigger-happy lawyers.

If I was in that position, I would probably write the editors of the existing Jones Magazine and ask for permission to use the name for your purposes. If they say yes, problem solved. If they say no, you probably dodged a bullet - you'd be much better off finding a new name early on than waiting until you magazine is successful (at which point you become an attractive lawsuit target) and then have to deal with transitioning to a new title with an active readership.